Biomass and nutrients in an Engelmann spruce–subalpine fir forest in north central Colorado: pools, annual production, and internal cycling

Abstract

Biomass and nutrient dynamics were examined in a subalpine Piceaengelmannii Parry–Abieslasiocarpa (Hook.) Nutt. forest within Loch Vale watershed in north central Colorado by quantifying annual above- and below-ground production, biomass, nutrient pools, and internal nutrient transfers. Subalpine forest covers only 6% of the watershed, and the values reported here refer only to the forested area. Total ecosystem biomass was 42 kg•m−2, of which 30% was soil organic matter, 33% was detrital biomass (including deadwood and forest floor), and 36% was living biomass. Total forest biomass (not including soil organic matter) was 28.9 kg•m−2, of which root biomass was 11%. Net primary production was 520 g•m−2•year−1, of which fine root production was about 27% and foliar production was 30%. Much more N was recycled via fine root turnover than via aboveground litter fall (1.6 versus 0.9 g•m−2•year−1), whereas four times more Ca was returned via litter fall than via fine roots. Compared with other temperate coniferous forests, this subalpine forest had low production. Nutrient resorption contributed between 35 and 38% of the annual requirements of N, P, and K, but only 9% of Ca and 12% of Mg. Although a higher percentage of annual N requirement was met by resorption, this forest used N less efficiently than a similar forest in southwestern Alberta.